There are typically three phases associated with taking a photo. These phases will herein be referred to as “Pre-Compose,” “Compose,” and “Shutter Release.” In each phase, the operator typically has many settings at their disposal to achieve the photo they desire.
Pre-Compose is the time before the photographer begins to compose the picture. This is usually not a time-critical phase, and the photographer adjusts common parameters such as:                Shooting mode: This is a setting that sets the camera for how many pictures to take upon release of the shutter from 1 picture per shutter release to continuous shooting while the shutter button is held down;        Bracketing: Where the camera takes multiple photos in succession at different exposures;        Focus modes: Selecting how the camera will focus. This typically ranges from a single small point to a wide area of the image and the camera finds the closest object and focuses on that. There are typically also settings to describe how the camera tracks the objects to focus, one time focus, etc.; and        Metering: Selecting how the computer in the camera analyzes what the camera is pointed at and calculates the exposure of the image. There are typically several different ways to tell the camera how to meter the exposure for the image.        
Compose is the time when the photographer composes the picture and is typically a very time critical phase. This typically starts when the photographer presses the shutter button halfway or pressing a button to start the metering and focus process. The camera then feeds back the level of exposure based on the settings of the camera. The photographer then adjusts the settings of the camera to expose the photo to the desired level. These settings typically include:                ISO: this is the setting for the sensitivity of the sensor to light. The higher the setting, the more sensitive the sensor is which allows taking an image in darker situations. However, this higher sensitivity often leads to artifacts (commonly referred to as noise) in the picture;        Shutter speed: This is the amount of time the shutter is open to expose the sensor to the light it needs to record the image. The faster the shutter speed, the less time the sensor is exposed, and the slower the shutter speed, the longer the sensor is exposed. This is dependent on the amount of light available. If there is little light then a longer exposure is needed. However, this often results in blurry shots because either the camera or the subject moves during the time the shutter is open. Sometimes this shutter is left open purposely to capture this motion or blur artistically;        Aperture: The aperture setting refers to the amount the lens is open to let in light. A very large aperture lets in the most light, but has the shortest depth of field (the amount of the image that is “in focus”). The smallest aperture has the largest depth of field, but lets in the least amount of light; and        Exposure: This controls how much the photographer would like to over or under expose an image typically to make sure the main subject is exposed correctly if there are very bright or dark subjects in the image affecting the exposure measurement.        
Shutter Release occurs when the photographer completely presses the shutter button and captures the image or images.
The primary parameters the photographer adjusts during photo shoots are what are called the pyramid of light: ISO, Aperture, and Shutter Speed. All three of these control how the light is used to compose the image. Adjusting any of these three elements affects the other two and photographers are constantly adjusting these three to get the image exposed how they desire in a crisp and clear image.
While many photographers prefer to set these settings themselves, many cameras have some form of “Automatic Mode” that uses the camera's intelligence to quickly make many of these setting decisions for the photographer. Nevertheless, photographers that want to exert more manual control than the “Automatic Mode” are continually adjusting these settings during their shots. Many cameras allow photographers to store settings that they wish to start with, usually in a menu or on the mode dial (sometimes called “Custom”), so that the photographer can quickly select the base settings they want to start with when they begin shooting. However, since the shots are always changing, the photographer has to move away from these base settings and quickly to adjust many of the parameters listed above for each shot.
The camera provides feedback to the photographer (typically in the viewfinder) about the exposure of the shot with the current settings, what the settings are, and then the photographer adjusts dials (or menus) to get the settings what they think they want, and take a shot. Then, typically the shooter looks at the shot on the built in screen on the camera to get an idea if the shot is what they desire and then usually they modify some settings and continue the shooting. However, most of the adjustments are made manually.
Some modes of operation try to “automate” these procedures. Modes like “aperture priority” and “shutter priority” allow the photographer to set one of the settings like aperture or shutter speed and then the camera does the adjustment of the other to maintain a properly exposed image. Some cameras even offer an automatic setting for ISO which even helps with the third leg of pyramid to allow the photographer to only have to adjust one of the three parameters. Such modes add convenience, but there remains a considerable amount of manual adjustment to be done during most shots. And since it is done manually by the photographer, it takes a significant amount of time when compared to the speed of the built-in camera computer that does this during automatic mode.